I'm not sure what you are asking. If the TV and the receiver both have ARC, then the theory is (reality != theory) that you can plug a source into a different input on your TV, and the audio from that source would feed back into your receiver. You don't reassign it or anything. Since there is one connection from the receiver to the TV, then the TV and receiver are supposed to automatically recognize that the TV is on a different input, and backfeed the audio to the A/V receiver.
So:
SOURCE->TV->RECEIVER becomes the audio pathway.